Radio-frequency transmission line switching system



W. TODD July 28, 1953 RADIO-FREQUENCY TRANSMISSION LINE SWITCHING SYSTEM Filed Feb. 5, 1946 RADIO REC EIVER FIG. 1.

INVENTOR WILLIAM TODD MMQ'M' i/far/re PULSE GENERATOR Patented July 28, 1953 RADIO-FREQUEN CY TRANSMISSION LINE SWITCHING SYSTEM William Todd, Neptune City, N. J assignor to the United States of America as represented by the Secretary of War Application February 5, 1946, Serial No. 645,685

6 Claims. (01. 333--97) (Granted under Title 35, U. S. Code (1952),

sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.v

The invention relates to electronic switches and to electronic switch control means.

In theelectronic art it is frequently necessary to render a transmission line alternately conductive and non-conductive at a very high alternation rate. Various mechanical switches have been devised, but it has been found impossible to devise a practical mechanical switch that will alternately open and close a transmission line in a few microseconds.

It is therefore an object of this invention to provide a switch of a novel character that will be extremely rapid in operation.

It is also an object of the invention to provide aswitch that will be stable in operation and that will require a minimum expenditure of power to operate the same.

These objects, together with other objects and advantages which will be apparent from a reading of the following specification, are attained, in a preferred embodiment of the invention, by means of a gas tube shunted across the free end of a half wave stub line of a main concentric transmission line. The characteristic of a half wave transmission line is such that when thefree end is open it behaves as a parallel resonant circuit and presents a high impedance, whereas when the free end is terminated, or shorted, it behaves as a series resonant circuit and presents a low impedance. Thus, when the gas tube is ionized, the free end of the stub line is shorted, and the stub line reflects a low impedance into the main transmission line which arrests the flow of radio-frequency energy therein. Electronic circuit means of a novel character are provided by the invention to alternately ionize and extinguish the gaseous discharge device at a very rapid rate and to maintain the current flow through the gas tube constant during conduction, whereby a constant impedance is presented.

For a better understanding of the invention, reference is made to the following specification of a preferred embodiment of the invention, the said specification to be read in conjunction with the accompanying drawings, in which,

Figure l is a schematic drawing of a preferred embodiment of the invention showing the invention applied as a switch between a dipole antenna and a radio receiver, and

Figure 2 is a schematic drawing showing the gas tube of Figure 1 together with a control apparatus in accordance with the invention.

antenna end of line I4.

Figure 1, a radio receiver I ll is connected-to a dipole antenna l2 through a main concentric transmission line l4 having a half wave length stub arm I6 one quarter of a wave length from the antenna, or input, end of line M. A gas tube l8, having electrodes 20 and 22, is positioned across the closed. end of the stub arm IS. The electrode 28 is grounded to the outer conductor and the electrode 22 is connected to the inner conductor of the arm [6. 24 is provided along the inner conductor of arm is between the electrode 22 and the transmission line It, and a quarter wave length radio frequency isolating stub 25 is formed integral with the outer conductor of the arm [6. The conductor 28 of stub 26 is connected to the inner conductor of arm l6 whereby connection may be made to the control apparatus of Figure 2,

It will be seen that when the gas tube is ionized,

radio frequency energy cannot flow in the concentric line [4 at the base of stub arm l6 since the low impedance which the gas tube l 8 presents' is reflected by the half wave stub arm Hi to that point, which results in a short circuit at the input- Thus when the gas tube is ionized the concentric line I4 is effectively switched closed, preventing the passage-of signal voltagefrom the antenna [2 to the 'rece'iver lli. I

The ionization of the gas tube [8 is controlled by voltage pulses from a square wave pulse generator 30 shown in Figure 2.

Referring now to Figure 2, a triode 32 is shown having its cathode 34 connected to the electrode 22 of the gas tube I8 and having its plate 36 connected to the grounded electrode 20 through a load 38 and a B supply battery 40. The grid 42 of the triode 32 is connected to the pulse generator 30 through a condenser 44. A grid resistor 46 is connected between the grid 42 and the oathode 3:3. The stray capacity of the system is in-:

dicated by a condenser 48 shown in broken lines and the radio frequency isolating stub 26 is represented by the radio frequency choke 26 shown in broken lines. The purpose of the stub 26 is to isolate transmission line [6 from the control apparatus and thus prevent the radio frequency energy on line [6 from leaking off through the control apparatus.

A square wave generated by the pulse generator 30 is applied across the grid resistor 46 in series with the condenser 44 and the stray capacity condenser 48. The flow of current through the grid resistor 46 is a differential curf rent wave, which current produces an instanta neous difference in potential between the cathode A blocking condenser 34 and the grid 42 of the triode 32. This difference in potential effectively reduces the internal resistance of the triode 32 and thereby raises the voltage across the gas tube l8. which results in its firing. Turn-off of the gas tube i8; is accomplished in the reverse manner; namely by applying the negative pip of the differential wave.

to the grid resistor 46.

The action of the triode 32 iSSilHllar to a normal current regulating discharge device, since the: action of the triode is to cause the gas tube IE to be either completely fired: or completely ex:

. device, and means connecting said differentitinguished. Although a triode 32 has been shown herein, it will be obvious that any multielement tube may be used.

It will be seen that the operation of the gas tube I8 is controlled by the relatively small amount of power generated by the pulse gerrerator 30. wave is sufiicient to cause the tube 8 to fire completely and the-negative pip is sufi'lcient to cause the. gas, tube to be completely extinguished. It will be noted that since a pulse generator is an essential part of most high frequency apparatus, a. minimum of extra equipment isused.

It, will be obvious that many modifications and changes might be made. For example, the branch arm {.6 could be a quarter wave length rather than a half wave length long, in. which case the. impedance characteristic of the switching operation would be reversed. It is. therefore intended that: the invention be defined by the following claims.

What is, claimed is:

1;. A radio. frequency switching system comprising acoaxial transmission line, a half wavelength coaxial stub; line having. its outer conductor at one endthereof connected to the outer conductor of said transmission line and having its inner conductor at saidone-endthereof connected to the inner conductor ofsaid transmission line; a gasi tube having: a first electrode connected to the outer conductor of said stub line at the-other end thereof and having a second electrode connected to the inner conductor of saidstub line at said; other end thereof; a source of plate voltage. of a. value at least sufficient to fire saidgas tube; an. electron discharge; device; a radio fre-- quencychoke connecting the cathode of said dervice. to; the, second-named electrode of said gas tuber means connecting. the plate of; said device to the first electrode of said gas tube through, said; source of. plate voltage; a grid resistor con,- necting the grid: of said device to said cathode; a condenser; a pulse generator connected to the grid of" said electron discharge device through said: condenser; said condenser and resistor constitutinga differentiating means for derivingv pulses. of opposite polarity, corresponding respectively tor the leading and trailing edges of each pulse from saidpulse generator, for firingthegas. tube at the leading edge and extinguishing the gas tube at the trailing edge of each pulse. from said pulse generator. I

2. A control circuit comprising a two-element gas discharge tube, a source of direct potential of a value at least sufiicient to-fire said gas dis-- charge tube, an electron discharge device havingat least a grid, a cathode, and-an anode, said electron discharge device being normally cut off,

said source of direct potential being connectedintermediate said anode and one element of said gas discharge tube and said cathode being con nected to the other-element of said gas dischargetube, a generator of substantially square wave The positive pip of the differential;-

ating means to said grid for supplying thereto saiddifierentiated pulses, thereby rendering said gas tube conductive at the leading edge of said square wave. pulse and non-conductive at the trailing edge. ofsaid square wave pulse.

3. A control circuit comprising a two-element gas discharge tube, a source of direct potential of a value at least sufficient to fire said gas discharge,- tube, an electron discharge device having at'least a grid, a cathode and an anode, said electrondischarge device being normally cut off,

said source of direct potential being connected intermediate said anodeand one element of said gas, discharge. tube, a radio; frequency choke connecting said cathode to the other element or? saidgas discharge tube. a generator of substantially square wave pulses,- and difierentiating means connected. intermediate said: pulse generator and said grid for deriving a positive-going diirerenti ated' pulse of sufiicient amplitude to rendersaid electron discharge device conductive from 'the leading edge of said square Wave pulse and: a negative-going differentiated pulse of sufiicient amplitude to cut off said electron discharge d'eedge thereof of' sufficientv amplitude to render" said vacuum tube conductive, and'aisecond' pulse coincident with the trailing edge thereof of sufiicient amplitude to cut off said; vacuum tube, and means connecting the output ofsaid differentiating circuit to the input of said vacuum tube.

5. Thecontrol circuit of claim 4, in. which said vacuum tube includes atleast a cathode, anode and control element and the output of: said did-- ferenti'ating: circuit is connected bet-weensaid control element and saidt cathode.

6; A radio frequency switching system compris ing a coaxial transmission line, a half wavelength coaxial stub line having its outer conductor at one end thereof connected to the outer-conductor of said transmission line at ground potential and having its inner con-ductorat' said one end thereof connected to the inner conductor of said transmission line, the point of junction of said stub line and said transmission line being; one quarterof a wavelength from the input. of said transmission-line; a gas tube having-a first electrode connected to the grounded outer conduc torof said stub line at the other end thereof and having asecond' electrode connected to the inner conductor of said stub line at said other end' thereof; a blocking condenser positioned along'saidinner conductor of. said stub line between said gas tube and: said transmission line, whereb direct current appearing across said gas tubemay be isolated, from, said transmission u line; a source ofplate voltage of'a value at least.

sufficient to fire said gas tube; a quarter wavelength coaxial stub line having one end of its outer conductor connected to the outer conductor of said half wavelength stub line intermediate said ends thereof; an electron discharge device having its cathode connected to the second-named electrode of said gas tube through the inner conductor of said quarter wavelength stub line, and having its plate connected to the grounded electrode of said gas tube through said source of plate voltage, and having a grid resistor connecting said grid and said cathode; a condenser; a pulse generator connected to the grid of said electron discharge device through said condenser; said condenser and resistor constituting a differentiating means for applying to the grid of said electron discharge device pulses of opposite polarity corresponding respectively to the leading and trailing edges of each pulse from said pulse generator.

WILLIAM TODD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,933,976 Hanson Nov, 7, 1933 1,966,216 Philpott July 10, 1934 2,140,003 Engl Dec. 13, 1938 2,189,549 Hershberger Feb. 6, 1940 2,203,882 Shore June 11, 1940 2,284,101 Robins May 26, 1942 2,405,843 Moe Aug. 13, 1946 2,408,425 Jenks Oct. 1, 1946 2,412,161 Patterson Dec. 3, 1946 2,442,304 Mayle May 25, 1948 2,505,534 Fiske Apr. 25, 1950 

